Since the advent of the audio cassette, portable audio players have enjoyed widespread popularity. Portable audio players allow a user to listen to audio data in virtually any setting by freeing the user from the mobility constraints imposed by bulky home-based stereo systems. Because portable audio players are often used in manner that makes connection to an external power supply impractical, portable audio players typically rely on batteries to provide power. Since such batteries have a limited lifetime, it is desirable for the audio player to consume as little power as possible. In addition, because portable audio players are often physically carried by the user, it is desirable to make the portable audio player's batteries small and lightweight.
Current portable audio players play digital audio data stored on a compact disk, or CD, which is manually loaded into the player by the user. CDs are capable of storing more data than cassette tapes and are less susceptible to degradation resulting from repeated use. In addition, CDs allow the user to jump quickly and automatically to different tracks of data, unlike cassette tapes, which require a magnetic tape to be physically spooled to the desired location, and typically do not contain indexing information to indicate where new tracks begin.
However, while CDs represent an improvement over audio cassette tapes, CDs still suffer from a limited amount of storage. For example, most present-day CDs are capable of storing at most 70 to 75 minutes of audio data. Moreover, many of the CDs that a user owns will contain even less data than this, since separate CDs are typically used to record separate programs and events. Even with the advent of the digital video disk, or DVD, with a much greater storage capacity than a traditional CD, it will typically be the case that a user will own a library of many different disks, each containing its own unique set of data. Thus, to listen to several hours of audio data, or to listen to a variety of programs, a user must carry several CDs and manually load the next CD into the player when the previous CD is finished playing. In addition, since CDs are relatively large, they require a relatively large portable unit to contain them. Another disadvantage of CDs is that the manner in which data is read from the disks is sensitive to physical shocks, which can cause undesirable discontinuities, or skips, in the audio output. In addition, power is consumed by continuously spinning the compact disk to obtain data.
The development of effective compression techniques has enabled a greater quantity of audio data to be stored in a much smaller amount of memory. For example, the MPEG audio layer 3 compression format, or MP3, is able to compress CD-quality digital audio data by a factor of about ten, and thus enables a CD-quality audio signal to be delivered at a data rate of 128 kilobits per second. As a result, these compression techniques make it practical for a compressed audio player to use storage media other than traditional cassettes or disks--media that would otherwise be prohibitively expensive to use. For example, the Rio MP3 Software Player, made be Diamond Multimedia, stores data in a 32 megabyte flash memory, a type of non-volatile electronic memory that allows for writing and erasing of data. By making use of compression techniques, a user can thus store approximately 30 minutes of audio data in the flash memory, whereas without compression, only about 3 minutes of audio data could be stored. However, current flash-memory-based portable audio players are only able to store about half as much data as a typical CD. As a result, whenever the user wants to listen to the data stored on a different CD, the user must manually copy that CD into the flash memory, a process which is much more time-consuming and cumbersome than simply loading a new CD into a traditional portable CD player. Although a flash memory can store additional audio data if a higher compression rate is used, higher compression rates can cause undesirable degradation of the audio data. In addition, flash memory is subject to fatigue, and will wear out after repeated write-erase cycles.
What is needed, then, is a portable player that makes use of a compact, high-capacity non-volatile storage medium, thus allowing the user to listen to a virtually unlimited supply of audio data without having to physically insert or copy additional data into the portable player's memory. While non-volatile magnetic media, such as the hard disk drives used in portable computers, have a large storage capacity, the amount of power that these hard disk drives consume makes them impractical for use in a portable audio player, which would either have to include an undesirably large battery, or have an undesirably short playtime. For example, while the 2.5" disk drives used in laptop computers are designed to consume relatively little power, their power consumption is still much greater than that which is acceptable in a typical CD-based portable audio player. Whereas a portable audio player may have a total battery weight of about 2 ounces, a laptop computer may have a battery weight of more than a pound. Thus, if a portable audio player were to use a hard disk in the same manner as a laptop computer, the battery life of the portable audio player would be prohibitively short.
Moreover, if the hard disk were turned off to conserve power, it would take a relatively long time to access data at a random location on the hard disk in comparison to the time necessary to access random data on a flash memory or CD. More specifically, from a powered off state, it typically takes three to six seconds to "spin up" and begin accessing data at a specified disk location. As a result, powering off the hard disk to conserve power would cause an undesirable delay between a user's request for audio data and the actual delivery of that data to the user.
Accordingly, it is an object of the present invention to provide a system and method for storing a large volume of audio data in a portable audio player. It is another object of the present invention to provide a system and method for reducing the power consumed by a portable audio player. Yet another object of the present invention is to provide a system and method for providing continuous, uninterrupted audio data to the listener.